Ten years ago, when the Microsoft billionaire Bill Gates was midway through his startling metamorphosis from monopolistic software magnate to possibly the world’s most admired philanthropist, he made a speech declaring that the traditional American high school was “obsolete”. Instead, his hugely generous charitable foundation invested $2bn in new, smaller schools for nearly 800,000 pupils.

But within a few years, in 2008, the funding abruptly stopped. Some of the schools had to close. Three years on, in one of his carefully rationed newspaper interviews, Gates explained: “The overall impact of the intervention, particularly the measure we care most about – whether [pupils] go to college – it didn’t move the needle much … We didn’t see a path to having a big impact, so we did a mea culpa on that.”

With its mix of idealism and cold jargon, its emphasis on charity needing to achieve dramatic results, and its slight underlying sense that Gates (pictured) wants to play God, this quote is one of many telling moments in Linsey McGoey’s fierce book. A former adviser to the World Health Organisation and a sociology lecturer at the University of Essex, long a base for radical academics, she casts an unsparing eye over “philanthrocapitalism” – as she and some of its practitioners call it. A small group of private donors, she writes, play “an outsized role in national and global policy-making”: they “want to revolutionise the last realm untouched by the hyper-competitive, profit-oriented world of financial capitalism: the world of charitable giving.”

Gates is currently the best known of these hard-nosed modern philanthropists, and the foundation that he and his wife, Melinda, run from a headquarters in Seattle the size of a large city block is the focus of about half this book. But first McGoey explores the thinking and methods of earlier conscience-stricken tycoons. Starting with John D Rockefeller Sr in the late 19th century, she shows that charity organised on business lines is not new, as philanthrocapitalists claim. Rockefeller was even advised by a man called Gates, Frederick T (no relation), a Baptist-minister-turned-management-guru preoccupied with how to give philanthropy the maximum “leverage” and “efficiency”.

McGoey also provocatively examines the power imbalances and ambiguities of charitable giving, “the difficulty of determining whose interests are most served”. While the Rockefellers were establishing their worldwide empire of good deeds, she points out, western anthropologists in Papua New Guinea were studying “‘Big Men’, tribal leaders who used gift-giving to accumulate well-placed friends, and expand trading jurisdictions”. In today’s global economy, where personal networking, reputation management and corporate social responsibility are constant preoccupations, charitable giving is more useful than ever. Philanthropy is a favourite topic when billionaires gather at Davos or a TED conference.

In 2009 McGoey attended another of these self-regarding summits, the annual Skoll World Forum in Oxford, established by Jeff Skoll, a self-styled philanthropist and social entrepreneur who made his fortune as an early eBay shareholder and employee. Her section on the event is too short, barely a couple of pages – you wonder if she was forbidden to take notes – but it does memorably include Skoll telling an audience of well-connected do-gooders, “You are a keystone species in the social change architecture.”

The Gates Foundation comes across better in the book. “The Gateses do considerable good,” McGoey concedes. “Like Melinda’s willingness to speak out about the importance of contraception ... in developing countries. Or Bill’s support for raising the capital gains tax in the US.” Echoing other analysts of modern tycoon philanthropy, she depicts the Gateses and their foundation as unusually “willing to change their minds when the evidence suggests they should. They don’t seem afraid to admit their mistakes.”

But one person’s flexibility is another’s cancelled funding. The book also details the downsides of the Gates approach to global health problems, an area where they spend more annually than many wealthy governments, including Germany. The foundation favours ambitious vaccines and disease eradication programmes. A persuasive array of health professionals cited by McGoey say these are squeezing out cheaper, quicker solutions. She also criticises the foundation’s choice of collaborators: not just farmers and small businessmen in poor countries but Goldman Sachs and Coca-Cola, Monsanto and Rupert Murdoch. Too much of the foundation’s money and activity, she argues, stays in the west.

And in the west few hold the Gateses to account. The last “serious” piece of US legislation regulating charitable foundations, she writes, was in 1969. Nowadays the ubiquity of the Gates organisation in the charity world, and beyond, means that few are prepared to attack it. McGoey’s interviewees are not plentiful, and mostly anonymous.

In the book’s later chapters, the relative even-handedness falls away. She condemns the “egotism” of Gates and other famous donors for “eponymously stamping their mark on their endowments”. She summarises with distaste the claim of some philanthropists (not Gates) that their giving is a form of “self-tax” that exempts them from paying other taxes. Most cuttingly, she says that philanthropy “thrives on … its own ineffectiveness” – in order to justify its own existence, charity needs the problems it addresses to persist.

These are all strong and rarely made arguments. But they feel a bit unforgiving. The highly personalised quality of the Gates Foundation, for example, is surely designed to open doors in a celebrity-driven world as much as it is to make Bill feel and look good. The book does not give as concrete a sense as it might of the foundation as an institution: what its headquarters feels like, how its confident staff talk. Access is not easily gained to either – when I profiled the foundation in 2010, it took months to sort out – and as an out-and-out Gates critic, McGoey may not have been willing or able; but she could have done more snooping around in Seattle.

This is a clear-eyed and much-needed study regardless. The super rich are all around us, but usually out of sight, arranging the world to their specifications. If this book shows what the relatively benign ones are up to, it makes you worry about the others.